Apparatus for supplying power to electrically heated catalyst converter

ABSTRACT

A catalyst heating apparatus includes an electrically heated catalyst converter mounted in an exhaust passage of an internal combustion engine, the catalyst converter having a catalyst and a heating element for electrically heating the catalyst so that catalytic conversion of exhaust gases from the engine is carried out, a capacitor that is charged with electric power, in advance, before an ignition switch is turned on for starting operation of the engine, and a controller for applying a terminal voltage of the capacitor to the heating element of the catalyst converter when the ignition switch is turned on, so that a temperature of the heating element is increased owing to electric energy supplied from the capacitor to the converter through the controller for accelerating the rate of the catalytic conversion of the exhaust gases.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention generally relates to a catalyst heating apparatus,and more particularly to an apparatus for supplying power to anelectrically heated catalyst converter mounted in an exhaust passage ofan internal combustion engine for catalytic conversion of exhaust gasesfrom the engine.

(2) Description of the Related Art

Conventionally, in an automotive vehicle, a catalyst converter ismounted in an exhaust passage of an internal combustion engine forcatalytic conversion of exhaust gases from the engine. Catalyticconversion signifies catalytic activity by a catalyst contained in thecatalyst converter for accelerating oxidization of carbon monoxide andhydrocarbon pollutants in the exhaust gases and/or reduction of oxygennitride pollutants in the exhaust gases. However, the catalytic activityor the catalytic conversion efficiency of a catalyst is relatively lowwhen the temperature of the catalyst is still low; before a certaintemperature level is reached. Once the engine starts operating, thetemperature of the catalyst gradually increases due to the heat ofexhaust gases passing into the exhaust passage, but if the engine is notwarmed up, during a cold start, for example, and the temperature ofexhaust gases is low, the temperature of the catalyst in the converterdoes not rise quickly to a required temperature level. Thus, there is aproblem in that the engine in such a condition exhibits a poor fuelcombustion efficiency, and the catalytic conversion efficiency of thecatalyst is low.

In the prior art, there is a disclosure of a catalyst converter. Forexample, Japanese Laid-Open Utility Model Application No. 49-36324discloses a conventional catalyst converter device for an internalcombustion engine. This catalyst converter device includes a heater or aheating element provided within a catalyst converter on its upstreamside in an exhaust passage of the engine. The heater, connected to acircuit of a starting motor of the engine, is energized when engineoperation is started by the starting motor, and serves to preheatunburned components in exhaust gases, for catalytic conversion of theexhaust gases before the catalyst converter is filled with exhaust gasesfrom the engine.

However, the above mentioned catalyst converter uses a battery as thepower source for supplying electric power to the heater of the catalystconverter. A resistance of the heater is constant with respect totemperature changes of the heater, and the electric power supplied bythe battery to the heater when the engine starts operating, especiallyduring a cold start, cannot be adjusted in the case of the abovecatalyst converter device. Thus, there is a problem, in the case of theconventional device, in that it is difficult to attain a rapid increaseof the temperature of the heater during a cold start of the engine, andin that it is difficult to shorten a time for the catalyst to heat upfor efficient catalytic conversion of exhaust gases.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providean improved catalyst heating apparatus in which the above describedproblems are eliminated.

Another and more specific object of the present invention is to providean apparatus for supplying power to an electrically heated catalystconverter, which apparatus can increase rapidly the temperature of theheater of the catalyst converter for efficient catalytic conversion ofexhaust gases from the engine. The above mentioned object of the presentinvention can be achieved by a catalyst heating apparatus which includesan electrically heated catalyst converter mounted in an exhaust passageof an internal combustion engine, the catalyst converter having acatalyst and a heater for electrically heating the catalyst so thatcatalytic conversion of exhaust gases from the engine is carried out, acapacitor that is charged with electric power, in advance, before anignition switch is turned on for starting operation of the engine, and acontroller for applying a terminal voltage of the capacitor to theheater of the catalyst converter when the ignition switch is turned ON,so that a temperature of the heater is increased owing to the electricenergy applied by the controller to the heater for accelerating the rateof the catalytic conversion of the exhaust gases. According to thepresent invention, it is possible to shorten a heat-up time of a heaterof a catalyst converter during a cold start of the engine and rapidlyincrease the temperature of the catalyst. A terminal voltage of thecharged capacitor is applied to the heater of the catalyst converterimmediately after the ignition switch is turned ON. It is possible topreset a terminal voltage of the charged capacitor of the inventionwhich voltage is higher than a voltage of electric power from thebattery initially applied to the heater of the conventional catalystconverter when the same amount of electric power is consumed in both theconverters.

Other objects and further features of the present invention will becomeapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a construction of a catalyst heatingapparatus according to the present invention;

FIG. 2 is a view showing an internal combustion engine in which thecatalyst heating apparatus of the present invention is mounted;

FIG. 3 is a view showing a detailed structure of the internal combustionengine, shown in FIG. 2, having the catalyst heating apparatus mountedtherein;

FIG. 4 is a flow chart for explaining the operations performed by thecatalyst heating apparatus of the present invention;

FIG. 5 is a time chart showing a relationship between the appliedvoltage of the heater and the terminal voltage of the capacitor;

FIG. 6 is a time chart showing a characteristic of the consumption powerof the heater of the catalyst converter; and

FIG. 7 is a diagram showing a catalyst heating apparatus in a secondembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, a description will be given of a construction of a catalystheating apparatus according to the present invention, with reference toFIG. 1. In FIG. 1, this catalyst heating apparatus includes anelectrically heated catalyst converter (EHC) 11 mounted in an exhaustpassage of an internal combustion engine. This catalyst converter (EHC)11 has a catalyst for performing catalytic conversion of exhaust gasesfrom the engine, and a heater for electrically heating the catalyst sothat the rate of catalytic conversion of the exhaust gases isaccelerated. The catalyst heating apparatus includes a capacitor 12which is charged with electric power in advance before an ignitionswitch in an automotive vehicle is turned ON, and a controller 13 forapplying a terminal voltage of the charged capacitor 12 to the heater ofthe catalyst converter 11 at least when the ignition switch is turnedON, so that a temperature of the heater is increased owing to theelectric energy applied by the controller to the heater for acceleratingthe rate of the catalytic conversion of the exhaust gases. According tothe present invention, a terminal voltage of the charged capacitor 12 isapplied to the heater of the electrically heated catalyst converter 11by means of the controller 13. In other words, the capacitor 12 is usedas the power source of the heater for electrically heating the catalystof the catalyst converter 11. The terminal voltage of the capacitor canbe adjusted to a level that is higher than a level of the constantvoltage of the battery used in the conventional converter when the sameamount of electric power is supplied in the both converters. Therefore,it is possible to rapidly increase the temperature of the catalyst up toa heat-up temperature level for a short time period by means of theheater which is suitably energized by the control of the controller 13.

Next, a description will be given of a first embodiment of the presentinvention, with reference to FIG. 2. FIG. 2 shows a construction of aninternal combustion engine to which a catalyst heating apparatus of thepresent invention is applied. In FIG. 2, those parts which are the sameas those corresponding parts shown in FIG. 1 are designated by the samereference numerals, and a description thereof will be omitted.

In FIG. 2, a battery 21 is a power source of an automotive vehicle whichsupplies electric power to a starting motor of an internal combustionengine 27 and to the controller 13 of the catalyst heating apparatuswhen an ignition switch of the vehicle is turned ON. An alternator 22generates electric power to be supplied to the battery 21, by convertingmechanical energy generated by the engine into electric energy. Theelectric power from the alternator 22 is supplied to the battery 21, sothat the electric power is stored in the battery 21.

In FIG. 2, a charge controller 24 supplies electric power received fromthe alternator 22 to the capacitor 12 based on detection signalsindicative of engine operating conditions, which signals are sent fromseveral sensors (not shown) to the charge controller 24. The sensorsinclude a water temperature sensor, a throttle position sensor and othersensors mounted on the internal combustion engine. When it is detectedby the detection signals that the quantity of electric power, generatedby the alternator 22, is smaller than a predetermined level, the chargecontroller 24 receives electric power from the alternator 22 andsupplies the same to the capacitor 12 via a diode 25 by increasing avoltage of the supplied power, so that the capacitor 12 is electricallycharged with the electric power from the charge controller 24. The diode25 is connected between the charge controller 24 and the capacitor 12for preventing a counterflow of electric current from the capacitor 12to the charge controller 24. This charge controller 24 also charges thecapacitor 12 when the engine stops operation, so that the quantity ofelectric energy required at a discharge of the capacitor 12 is stored inadvance when the ignition switch is turned ON.

As described above, a terminal voltage of the charged capacitor 12 isapplied to the EHC 11 through the controller 13 so that the heater ofthe EHC 1 receives electric power for heating the catalyst of the EHC11. The capacitor 12 at this time serves as the power source supplyingpower to the EHC 11, which replaces the battery supplying power to theheater of the conventional converter. An air injection pump (AI Pump) 26is mounted in the engine for sending a secondary air to the exhaustpassage upstream of the EHC 11, and the supplying of the secondary airis controlled by the controller 13. The catalytic conversion of exhaustgases passing through the exhaust passage is carried out by the EHC 11together with this secondary air supplied by the AI pump 26, and therate of the catalytic conversion is accelerated by thermal energysupplied through the heater of the EHC 11.

FIG. 3 shows a detailed structure of the internal combustion engine inwhich the electrically heated catalyst converter is mounted. As shown inFIG. 3, an air inlet 29 is formed in the exhaust passage at a portioncorresponding to the outlet of an exhaust manifold 28 of the engine,and, from the air inlet 29 a secondary air from the AI pump 26 is sentto exhaust gases passing through the exhaust passage. Downstream of theair inlet 27 in the exhaust passage of the engine 27, the electricallyheated catalyst converter 11 according to the invention is provided.This catalyst converter 11 is made up of, for example, an electricallyconductive metal monolith substrate with alumina coating, or anelectrically heated monolith substrate on which a platinum catalyst isformed. Provided in a neighborhood of the EHC 11 in the exhaust passageare; a temperature sensor 30 which is formed with thermocouples andconnected to the EHC 11 for detecting a temperature of a heating elementof the EHC 11, a connecting wire 31 connected to a terminal of the EHC11, and a connecting wire 32 connected to a terminal of the EHC 11through which electric power from the battery is supplied to the EHC 11via the controller 13. Also, a main catalyst converter 33 for catalyticconversion of exhaust gases is provided, separately from the EHC 11, inthe exhaust passage downstream of the EHC 11.

FIG. 4 shows operations performed by the catalyst heating apparatusshown in FIG. 2. In step 101 of the flow chart shown, an ignition switchin an automotive vehicle is turned ON. In step 102, a voltage at aterminal of the battery 21 is checked to ascertain whether or not thevoltage of the battery is lower than a given normal level. If thebattery voltage is higher than the given level, the battery 21 is innormal condition and step 103 applies a terminal voltage of thecapacitor 12 to the heater of the EHC 11 through the controller 13.Normally, the capacitor 12 is charged with electric power in advancebefore the ignition switch is turned ON. Provision of the capacitor 12enables a level of electric power initially supplied to the EHC 11 to bemuch higher than a level of electric power supplied directly from thebattery as in the conventional converter.

In step 104, a judgment is made based on a detection signal sent by thetemperature sensor 30 to the controller 13 whether or not the detectiontemperature of the heater of the EHC 11 is higher than a predeterminedtemperature level. This temperature level is preset in view of acatalyst activation temperature which corresponds to a temperature atwhich the catalyst of the EHC 11 reaches a catalyst activation level. Ifthe detection temperature of the heater is not higher than thispredetermined level, the procedure returns back to the step 103 so thatthe electric power from the charged capacitor 12 is again supplied tothe heater of the EHC 11. If the detected temperature of the heater ishigher than the predetermined level, step 105 stops supplying electricpower to the EHC 11, and immediately after the step 105, step 106 startsthe engine operation. In the step 102 above, if it is detected that thebattery voltage is lower than the prescribed level, step 107 gives awarning of a battery malfunction which may take place in the battery 21.After the step 107, the step 106 starts the engine operation withoutsupplying the electric power to the EHC 11.

After the engine starts operation, step 108 allows a secondary air toenter the exhaust passage of the engine at a portion upstream of the EHC11 by operating the AI pump 26 when the engine is in a given operatingcondition. This given operating condition is, for example, a conditionwhen an air-fuel ratio feedback control is still not performed. Thesecondary air is mixed with exhaust gases from the exhaust manifold 28of the engine, and the catalytic conversion of exhaust gases is carriedout together with the secondary air when they pass through the EHC 11and the main catalyst converter 33 downstream of the EHC 11 in theexhaust passage. By means of the catalyst in the EHC 11 and the maincatalyst converter 33, unburned components of exhaust gases includingcarbon monoxide, hydrocarbon, and oxygen nitride pollutants areconverted through oxidization and reduction, and the rate of catalyticconversion is accelerated by the secondary air. Thus, according to thepresent invention, it is possible to attain a high catalytic conversionefficiency.

Since the secondary air supplied by the AI pump 26 enters the exhaustpassage in the step 108, the temperature of the heater of the EHC 11 issomewhat lowered. In step 109, a terminal voltage of the capacitor 12 isagain applied to the heater of the EHC 11 under control of thecontroller 13. Similarly, step 110 judges whether or not the temperatureof the heater of the EHC 11 is higher than a predetermined temperaturelevel. The supply of the electric power to the EHC 11 is repeated untilthe heater temperature rises to such a predetermined level correspondingto a catalyst activation temperature. When the temperature of the heaterof the EHC 11 is higher than the predetermined level, step 111 stopsapplying a terminal voltage of the capacitor 12 to the EHC 11.

The above described procedure (steps 101 through 111 in FIG. 4) iscarried out each time the engine operation is started by turning theignition switch ON. After the engine started operation, the chargecontroller 24 serves to supply electric energy, generated by thealternator 22, to the capacitor 12 via the diode 25 in a way that theengine is not subjected to a great load at a time. And, the capacitor 12is charged with the electric power supplied thereto.

FIG. 5 shows a time chart which indicates changes in the terminalvoltage of the capacitor 12 and the applied voltage of the EHC 11 withrespect to the elapsed time since the ignition switch is turned ON. Forthe sake of convenience, assume that the resistance of the EHC 11 is0.01 ohm, the resistance of the connecting wire between the EHC 11 andthe capacitor 12 is 0.003 ohm, and the voltage drop in the controller 13is 1.4 volt constant. In the case shown in FIG. 5, it is assumed thatthe amount of electric power, which is substantially the same as that ofthe conventional converter in which electric power of 4,000 W from thebattery is applied directly to the heater in approx. 20 seconds, issupplied to the heater of the EHC 11. As shown in FIG. 5, the terminalvoltage (indicated by "Vt" in FIG. 5) of the capacitor 12 shows themaximum level at a time when the ignition switch has just been ON (theelapsed time t=0), and the terminal voltage Vt is gradually changed ininverse proportion with respect to the elapsed time since the ignitionswitch was turned ON. The applied voltage (indicated by "Va" in FIG. 5)when the terminal voltage Vt of the capacitor 12 is actually applied tothe EHC 11 shows the maximum level (which is lower than the maximumlevel of the terminal voltage Vt) at a time when the ignition switch hasbeen just turned ON, and is changed in inverse proportion with respectto the elapsed time.

In a case of the conventional converter, the electric power suppliedfrom the battery to the catalyst converter, and the consumption power Wconsumed in the converter is, for example, 4000 W constant with respectto the elapsed time and it cannot be adjusted. In this embodiment of theinvention, the consumption power W consumed in the EHC 11, which poweris represented by W=Va² /0.01 (the resistance of the EHC: 0.01 ohm),shows the maximum level when the ignition switch has just been turned ON(t=0) similarly. As can be seen from FIG. 6, the EHC 11 shows a highconsumption power (approx. 9000 W) at the ignition-ON time (t=0), whichis much higher than that of the consumption power W in the conventionalcatalyst converter. Subsequently, the consumption power W is graduallydecreased with respect to the elapsed time. However, it should be notedthat in approx. 10 seconds since the ignition switch is turned ON, theamount of electric power supplied to the EHC 11 of the invention isgreater than that of the corresponding power in the conventionalconverter. Thus, according to the present invention, it is possible tosupply a great amount of electric power to the EHC 11 during thestarting operation of the engine, thus allowing a rapid increase of thetemperature of the EHC 11 after the ignition switch was turned ON.

It should be noted that the electrically heated catalyst converter (EHC)11 of the invention does not easily break because it is maintained at arelatively low temperature if a great amount of electric current flowsacross the converter 11. The time for the catalyst to be in a heat-upcondition is thus shortened, and it is possible to reduce the heatdissipation of the heater of the converter.

Next, a description will be given of a second embodiment of the presentinvention, with reference to FIG. 7. In FIG. 7, those parts which arethe same as those corresponding parts in FIG. 2 are designated by thesame reference numerals, and a description thereof will be omitted. Acatalyst heating apparatus shown in FIG. 7 includes a capacitor 40corresponding to the capacitor 12 in FIG. 2, a controller 41corresponding to the controller 13, and a pair of switching members SW1and SW2 connected at both ends of the capacitor 40. The capacitor 40 canstore a relatively great amount of capacitance and has a withstandingvoltage of 1 to 3 volts. In a modified catalyst heating apparatus, a setof capacitors connected in series one another would be used instead ofthe above capacitor 40, so that a higher voltage is generated due toelectric power stored in the set of capacitors. Each of the switchingmembers has two connection points "a" and "b", and both the switchingmembers SW1 and SW2 are together connected to selectively one of thecorresponding connection points "a" and "b". The connection point "a" ofthe switching member SW1 is coupled to a terminal of the diode 25, andthe connection point "b" thereof is coupled to a heater terminal of theEHC 11. The connection point "a" of the switching member SW2 isgrounded, and the connection point "b" thereof is coupled to a terminalof the alternator 22.

In the catalyst heating apparatus shown in FIG. 7, the switching membersSW1 and SW2 are normally connected to the connection point "a" under thecontrol of the controller 41. Thus, a terminal voltage of the alternator22 is applied to the capacitor 40 through the charge controller 24 viathe switching member SW1 so that the capacitor 40 is charged withelectric energy generated by the alternator 22.

After the ignition switch is turned ON, the controller 41 permits,before the engine starts operating, an electrical connection between thecapacitor 40 and the converter 11 by connecting the switch SWl to theconnection point "b", coupled to the EHC 11, and connecting the switchSW2 to the connection point "b", coupled to the alternator 22 and thebattery 21. A terminal voltage of the charged capacitor 40 is applied tothe EHC 11 via the switch SWl, so that a temperature of the heatingelement of the EHC 11 is increased owing to the electric power suppliedfrom the capacitor 40.

When it is detected, in response to the detection signal from thetemperature sensor 30, that the temperature of the heater of the EHC 11is higher than a predetermined temperature level corresponding to acatalyst activation temperature, the controller 41 permits an electricalconnection between the capacitor 40 and the charge controller 21 byconnecting the switch SW1 to the connection point "a", coupled to aterminal of the diode 25 connected to the charge controller 24, andconnecting the switch SW2 to the connection point "a" connected to aground. The application of the terminal voltage of the capacitor 40 tothe converter 11 is thus stopped, and at the same time the capacitor 40is charged with electric power from the alternator 22.

In this second embodiment of the invention, the catalyst heatingapparatus includes an air injection pump (not shown) for sending asecondary air into the exhaust passage of the engine upstream of the EHC11, which is the same as the air injection pump 26 shown in FIG. 2. Thecatalyst heating apparatus shown in FIG. 7 also includes a temperaturesensor (not shown) for generating a signal indicative of a temperatureof the heating element of the EHC 11, which is the same as thetemperature sensor 30 shown in FIG. 3. It should be noted that almostall the electric energy stored in the capacitor 40 can be used forincreasing a temperature of the heating element of the EHC 11, and thatthe initial voltage applied to the EHC 11 can be easily preset to a highlevel, allowing a rapid increase of the temperature of the heatingelement of the EHC 11.

Further, the present invention is not limited to the above describedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention.

What is claimed is:
 1. A catalyst heating apparatus comprising:anelectrically heated catalyst converter mounted in an exhaust passage ofan internal combustion engine, said catalyst converter having a catalystand a heater for electrically heating said catalyst so that catalyticconversion of exhaust gases from said engine is carried out; a capacitorthat is charged with electric power, in advance, before an ignitionswitch is turned on for starting operation of the engine; and controlmeans for applying a terminal voltage of said capacitor to said heaterof said catalyst converter when the ignition switch is turned ON, sothat a temperature of said heater is increased owing to the electricenergy applied by said control means to said heater for accelerating therate of the catalytic conversion of the exhaust gases.
 2. A catalystheating apparatus as claimed in claim 1, wherein said control meansstops applying a terminal voltage of said capacitor to said heater ofsaid converter when it is detected that a temperature of said heater ishigher than a predetermined level, said predetermined levelcorresponding to a temperature at which said catalyst reaches acatalytic activation condition.
 3. A catalyst heating apparatus asclaimed in claim 1, further comprising detection means for generating asignal indicative of a temperature of said heating element, said controlmeans continuing to apply a terminal voltage of said capacitor to saidconverter when it is detected, in response to the signal generated bysaid detection means, that the temperature of said heating element ishigher than a predetermined level corresponding to a temperature of atwhich said catalyst reaches a catalytic activation condition.
 4. Acatalyst heating apparatus as claimed in claim 1, further comprising anair injection pump that sends a secondary air into the exhaust passageof the engine upstream of said converter when the engine is in a givenoperating condition after the engine operation is started.
 5. A catalystheating apparatus as claimed in claim 4, wherein said control meansapplies a terminal voltage of said capacitor to said converter after asecondary air is sent by said air injection pump into the exhaustpassage.
 6. A catalyst heating apparatus as claimed in claim 1, furthercomprising a pair of switches, provided at both ends of said capacitor,an alternator and a charge controller controlling an output of electricpower supplied from said alternator, said control means, before theignition switch is turned on, permitting an electrical connectionbetween said capacitor and said charge controller by connecting one ofsaid switches to a connection point coupled to a terminal of said chargecontroller, and connecting the other switch to a connection pointconnected to a ground, said capacitor thus being charged, in advance,with electrical power supplied from said alternator through said chargecontroller.
 7. A catalyst heating apparatus as claimed in claim 6,wherein said control means, after the ignition switch is turned on,permits an electrical connection between said capacitor and saidconverter by connecting one of said switches to a connection pointcoupled to said converter, and connecting the other switch to aconnection point coupled to said alternator, so that a temperature ofsaid heating element is increased owing to electric power being suppliedfrom said capacitor to said converter through said control means.
 8. Acatalyst heating apparatus as claimed in claim 6, wherein said controlmeans stops applying a terminal voltage of said capacitor to saidconverter when it is detected that a temperature of said heating elementis higher than a predetermined level, said predetermined levelcorresponding to a temperature at which said catalyst reaches acatalytic activation condition.
 9. A catalyst heating apparatus asclaimed in claim 6, further comprising an air injection pump which sendsa secondary air into the exhaust passage of the engine upstream of saidconverter when the engine is in a given operating condition after theengine operation is started.
 10. A catalyst heating apparatus as claimedin claim 6, further comprising detection means for generating a signalindicative of a temperature of said heating element, said control meanscontinuing to apply a terminal voltage of said capacitor to saidconverter when it is detected, in response to the signal generated bysaid detection means, that the temperature of said heating element isnot higher than a predetermined level corresponding to a temperature atwhich said catalyst reaches a catalyst activation condition.